1. Field of the Invention
The present invention relates to an extraneous substance inspection method and apparatus and, more specifically, relates to an extraneous substance inspection method and apparatus for semiconductor wafers in which a moving range of an inspection table is reduced to thereby limit the size of the inspection table and to improve the inspection efficiency.
2. Background Art
There are two types of extraneous substance inspection apparatus for semiconductor wafers (hereinafter simply called as wafer or wafers), one is that which employs an XY scanning method in which laser beam is irradiated over the surface of a wafer so as to scan the same in X and Y directions, and the other is that which employs a rotating scanning method in which laser beam is irradiated over the surface of a wafer while rotating the same so as to scan the same in a manner of a spiral shape or a concentric circular shape.
In the former XY scanning, for example, an inspection table is moved in X direction for performing a main scanning, and laser beam or further the inspection table is moved in Y direction for performing a subscanning. The main scanning in X direction is normally a reciprocating scanning in order to enhance the scanning speed. Although the XY scanning method poses a problem of requiring a long time for scanning over the entire surface of a wafer, however, has advantages that the detection accuracy at individual detection areas is invariable and comparatively small extraneous substances can be detected with accurate locations thereof. On the other hand, in the latter scanning method since the circumferential velocities at the outer circumference on a wafer and at the center portion thereon are different, the latter poses a problem with regard to non-uniform detection at the individual detection areas that the scanning density at the outer circumferences is rough, and the scanning density at the center portion thereof is dense and further the detection areas therearound overlap each other, however the latter has an advantage that the time required for the scanning over entire surface of the wafer is shortened.
In these days, in association with the improvement in integration degree of ICs an improvement in inspection accuracy of a wafer is demanded. In connection thereto, the XY scanning method tends to be used for performing the extraneous substance inspection for wafers. However, when an extraneous substance inspection is performed in a semiconductor manufacturing process line by incorporating therein an extraneous substance inspection apparatus employing an XY scanning method, the through-put due to the inspection reduces and, in addition, a drawback of increasing the size of the apparatus is caused which will be explained below.
FIG. 5 is a view for explaining a moving range of an inspection table in a conventional extraneous substance inspection apparatus employing an XY scanning method. A wafer 1 is carried on the inspection table, however, in the drawing the moving range of the inspection table is explained by making use of the movement of the wafer 1.
When assuming that an extraneous substance inspection optical system 2 is set at the position as illustrated, in order to scan the entire surface of the wafer 1 it is necessary to move the wafer 1 with the inspection table in such a manner that the center 0 of the wafer 1 moves in X direction from axis X1 to X2. With regard to Y direction the wafer 1 has to be moved with the inspection table in such a manner that the center 0 of the wafer 1 moves a distance corresponding to that from axis Y1 to axis Y2.
Accordingly, when assuming that the diameter of the wafer 1 is D, if the inspection table carrying the wafer 1 does not cover at least a range 2D.times.2D, in that logitudinally 2D and laterally 2D, the entire surface scanning through the movement of the wafer can not be achieved. For this reason, it is necessary to enlarge the size of the movement mechanism for the extraneous substance inspection table at least more than the range of 2D.times.2D. Therefore, it was inavoidable to increase the size of the apparatus including the inspection table. In particular, there arises a problem that the size of the apparatus increases corresponding to the increase of the outer diameter of the wafer 1.
On the other hand, instead of moving the wafer 1 if the extraneous substance inspection optical system is moved to scan the wafer 1, the moving range of the scanning system decreases. However, because the extraneous substance inspection optical system includes a lot of lenses therein, a high speed movement of the extraneous substance inspection optical system itself likely causes such as a positional displacement and vibration of the optical system which disturbs an accurate extraneous substance detection. Further, in view of the size and weight of the optical system such high speed movement is not preferable.
Different from the above measure there is another method in which a wafer is scanned by swinging laser beam, however, such method increases the scale of the scanning optical system and the entire size of the apparatus inavoidable increases.